Pre-manufactured trusses are often used in the construction of modern structures. Roof trusses and floor trusses, for example, can be manufactured to the correct specifications at a factory and then shipped to the construction site. Because they are pre-manufactured, the trusses can be installed quickly and easily. Moreover, the trusses can be engineered at the factory to provide the necessary strength with a minimal amount of material.
Each truss comprises a collection of wood pieces held together by truss plates embedded in the wood at the intersections of the pieces. A truss plate comprises a square or rectangular piece of metal sheet having a plurality of projections extending from one side thereof and is pressed into an intersection of two or more wood pieces so that a substantial number of the projections of the truss plate are pressed into each of the wood pieces. Precise alignment of the truss plates is necessary; however, with this type of apparatus the wood pieces can be joined together quickly and easily to thereby form a strong truss.
A gantry press is often used to help automate the manufacture of these trusses by pressing the truss plates into the wood pieces. The various wood pieces are first cut and then positioned on a platform in the desired configuration. The truss plates are placed in the appropriate positions on top of and beneath the intersections of the wood pieces and the gantry press is then rolled over the partially completed truss to press all of the truss plates into the wood. The gantry press typically presses the truss plates into the wood pieces to a depth of 50-80% of the total length of the projections. Accordingly, the truss may then be passed through a final press, which comprises a pair of nip rollers, to firmly embed the truss plates in the wood pieces.
The typical gantry press includes a movable gantry frame mounted on two guide tracks extending along each side of the platform. A roller is carried by the gantry frame at a predetermined distance above the platform surface so that, as the gantry frame is moved along the guide tracks, the roller presses the truss plates into the wood pieces.
In truss manufacturing it is desirable to remove the truss from a desired end of the platform once the truss plates have been pressed. After the gantry frame has traveled along the length of the platform, it is parked at one end and the truss may be removed from an opposite end. However, the vertical position of the roller relative to the platform prevents the truss from being removed from the end of the platform where the gantry frame is parked. Accordingly, to allow all of the trusses to be removed from the desired end of the platform, one approach is to make two passes with the gantry frame, which slows production. The truss cannot be removed from the table, and the assembly of another truss begun, until the return pass has been completed.
Several approaches have attempted to solve this problem by providing a truss manufacturing apparatus where only one pass of the gantry frame is required for each truss. One approach incorporates guide tracks which are inclined beyond the desired end of the platform. Thus, as the gantry frame is moved beyond the end of the platform it is also raised so that the completed truss may be passed under the roller for removal. This approach, however, requires guide tracks which extend substantially past the end of the platform to provide the necessary amount of incline and thus is disadvantageous in manufacturing facilities where floor space is limited.
A second approach incorporates a lifting device for raising the roller from its supports in the gantry frame so that the completed truss can be removed by being passed under the roller. This approach, however, may not sufficiently maintain the predetermined distance between the bottom of the roller and platform, which is important for proper truss formation. Each raising and lowering operation may cause the roller to be misaligned relative to the gantry frame and therefore also misaligned relative to the platform. Accordingly, the truss plates may not be properly pressed into the wood, which can be detrimental to the trusses.
In addition, it is desirable with gantry presses to perform periodic maintenance such as lubrication of the various moving parts or resurfacing or replacement of the gantry roller. However, with conventional gantry presses it is difficult to obtain access to the gantry frame and roller because of their proximity to the platform. Moreover, conventional gantry presses are fixed in position relative to the platform so that the production of trusses must be halted while the maintenance is performed.